Convert Gear Diametral Pitch To Module.

Jim Petridis

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Hello there,
I wonder if someone can help me. I have to a gear with 28 teeth and a 1.666"diameter. I want to cut an identical gear. I worked out that it has an 18.05 Diametral pitch. Converting it to module with my calculations it is a 1.4066 modul. My question is: should I use a 1.5 module or am I wrong? To get imperial cutters are very expensive, but the metric are cheaper.
Thank you
Jim
 
I suspect you have an 18dp gear there, it's a fairly common size and 1.4mod isn't!
If it were a 1.4 mod gear, a 1.5 cutter would give oversize spaces, undersize teeth and generally poor tooth profiles.
Taking 18dp and 28 teeth, the overall diameter (over the teeth) will be 30 (allowing for the addenda) / 18 or 1.666, which is what you measured?

Next you need to find the gear's pressure angle (pa), an easy way is to roll the gear on a slab of plasticine and measure the included angle of the plasticine rack generated, either 29 degrees (14.5 degree pressure angle) or 40 (20pa).

Gear cutters only cut a small range of tooth-counts, as they cut the different profiles required for thedifferent tooth-counts so you'll need one of the set...
 
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Hello Jim, I have just read your post, and by now you may have found your answer to your question regarding the use of a module 1.5 cutter to make your imperial gear. I am by no means an expert at all as I have never cut a gear myself and all I have done is search the internet for information to study all the aspects of gear cutting for myself. But if you go to the following web site you can download free software that calculates up to 26 parameters for you. I input two of your values, 18dp which "Brittish Steel" mentioned and 28 teeth. The calculator returns as one of the calculations, a diameter of 1.666" which is what you had indicated, then I did the same again but entered a module of 1.5 instead and chose the imperial calculation and it returns with a diameter of 1.771"
 
Hi again Jim, I hit the wrong key and my unfinished reply got posted. the web site for "GEAR SPEC" http://www.wmberg.com
This site has a lot of calculators and info. BTW I also inputt a module of 1.25 and the diameter of the gear was less than your figure of 1.666".
Kind regards Basil
 
I suspect you have an 18dp gear there, it's a fairly common size and 1.4mod isn't!
If it were a 1.4 mod gear, a 1.5 cutter would give oversize spaces, undersize teeth and generally poor tooth profiles.
Taking 18dp and 28 teeth, the overall diameter (over the teeth) will be 30 (allowing for the addenda) / 18 or 1.666, which is what you measured?

Next you need to find the gear's pressure angle (pa), an easy way is to roll the gear on a slab of plasticine and measure the included angle of the plasticine rack generated, either 29 degrees (14.5 degree pressure angle) or 40 (20pa).

Gear cutters only cut a small range of tooth-counts, as they cut the different profiles required for thedifferent tooth-counts so you'll need one of the set...
I suspect you have an 18dp gear there, it's a fairly common size and 1.4mod isn't!
If it were a 1.4 mod gear, a 1.5 cutter would give oversize spaces, undersize teeth and generally poor tooth profiles.
Taking 18dp and 28 teeth, the overall diameter (over the teeth) will be 30 (allowing for the addenda) / 18 or 1.666, which is what you measured?

Next you need to find the gear's pressure angle (pa), an easy way is to roll the gear on a slab of plasticine and measure the included angle of the plasticine rack generated, either 29 degrees (14.5 degree pressure angle) or 40 (20pa).

Gear cutters only cut a small range of tooth-counts, as they cut the different profiles required for thedifferent tooth-counts so you'll need one of the set...
Thank you for the help. I should have to do more calculations to find out what modul
I need to cut an 18 diametral pitch.
 
Hi again Jim, I hit the wrong key and my unfinished reply got posted. the web site for "GEAR SPEC" http://www.wmberg.com
This site has a lot of calculators and info. BTW I also inputt a module of 1.25 and the diameter of the gear was less than your figure of 1.666".
Kind regards Basil
Thanks Basil for the site you sent me. I shall check it and let you know how I went.
 
Jim, I don't think a module cutter is likely to give a good result, two reasons:

first the tooth size will be wrong, 18dp is 1.411 mod, not something that anyone manufactures; 1.5 mod is a standard, but that's closer to 17dp and the gear's won't run together well (a bit like putting a 16tpi bolt in a 18 tpi nut: jamming, stripping and eventually failing).

second, module pitch gears are invariably 20 degree pressure angle, dp can be either 14.5 or 20 (or oddballs), the wrong pa will give both excessive wear, noisy operation and tooth-frequency speed variations that transfer to the work finish. That's three things...

Mixing the two is a Bad Idea, either buy the right (dp and pitch angle) cutter, even if it's more expensive OR buy the gear/s you need.
 
Jim, I don't think a module cutter is likely to give a good result, two reasons:

first the tooth size will be wrong, 18dp is 1.411 mod, not something that anyone manufactures; 1.5 mod is a standard, but that's closer to 17dp and the gear's won't run together well (a bit like putting a 16tpi bolt in a 18 tpi nut: jamming, stripping and eventually failing).

second, module pitch gears are invariably 20 degree pressure angle, dp can be either 14.5 or 20 (or oddballs), the wrong pa will give both excessive wear, noisy operation and tooth-frequency speed variations that transfer to the work finish. That's three things...

Mixing the two is a Bad Idea, either buy the right (dp and pitch angle) cutter, even if it's more expensive OR buy the gear/s you need.
Thank you for the good advice. You answered my question.I shall buy another gear.
Still learning.
Jim p
 
Ok this is a little "old" but I thought it might be useful to add to the information already here....

1) There really is no difference between DP, CP and Module gear teeth, it's just another way of writing the same thing, ie DP10 is also MOD2.54
2) PA, these are available in any angle you may want, but the norm is 14.5, 20, 25, 27 and 30
3) Always look to create gears with prime number teeth count to reduce the "hunting tooth combination"

Google search "convert from DP to module.. but also google none circular gears :)
 
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